The size-dependent optoelectrical properties of semiconductor nanocrystals (NCs) hold great promise for device applications such as photovoltaics, light-emitting diodes, and photodetectors. Additionally, the prospect of films cast from colloidal solutions of these semiconductor nanocrystals offers a cost-efficient and scalable deposition technique with the potential for widespread application.
Group II-VI and IV-VI compound semiconductors have dominated the field of nanocrystal thin films owing to well-established solution-phase synthesis processes. The process results in a sterically stabilized colloidal dispersion from which ligand-capped nanocrystals will naturally self-assemble when cast into a film. Post-processing to remove or exchange the electrically-insulating ligands is typically done in order to form a more dense, electronically-coupled nanocrystal film.
The scarcity and toxicity of many Group II-VI and IV-VI semiconductor materials make silicon a more attractive material. However, solution synthesis of silicon nanocrystals has proven difficult due to the high temperatures needed. Nonthermal plasma synthesis of Si and Ge nanocrystals as an effective alternative to typical solution techniques has been previously demonstrated.
Nonthermal plasma synthesis will uniquely produce free-standing, or bare, nanocrystals. The well-developed method of decomposing silane as the silicon source results in an H-terminated nanocrystal surface. Unfortunately, efforts to disperse H-terminated Si nanocrystals in solvents have been unsuccessful. Stable suspensions have been achieved, but they ultimately lead to poor film quality.
Thus, there remains a need in the art for high quality silicon nanocrystal films and methods of making the same.